Frequently, additional biologically-active substances must be administered to animals raised and kept for the production of e.g. meat, milk, wool or eggs, e.g. for supplying them with amino acids supplements, vitamins or veterinarily active substances. This generally poses no problems in the case of monogastric animals because the active substances to be supplied to them can be quite simply administered orally, e.g. mixed into the feed as an additive or in the form of gelatin capsules containing the active substance. However, such simple methods generally fail in the case of ruminants because the active substances to be supplied are metabolized at least for the most part in the rumen by the rumen flora and, in any case, are available in a low amount for direct resorption in the following intestinal tract. If a delayed release of the active substance is desired in addition thereto, this poses problems even in monogastric animals, especially when a large dose must be administered, since the active substance is generally either bound to a matrix or is embedded in a matrix and the matrix can usually contain only a small amount of the active substance. Also, diffusion-controlled release of active substances is difficult to coordinate and is hardly suitable for administering large amounts of active substance. Also to be considered is the cost of preparing the dosage forms.
An almost limitless number of suggestions have already been made for solving these problems. They all have in common the fact that the active substance to be supplied is protected against premature release in the rumen or the stomach by embedding it in a matrix or by surrounding it with a coating. A variety of materials can be used for the matrix or the coating. However, none of the known suggested solutions is completely satisfactory because substances must be used as component for the protective materials which are either not legally acceptable for ruminant nutrition or at least not yet or are not readily available, require an expensive pretreatment or the particles prepared with their help tend to adhere during storage and/or are thermally and mechanically not sufficiently stable.